What is meaning of Non-Fermi liquid?

Answer 1

Non-Fermi liquid (NFL) is a metallic state which deviates from Fermi liquid theory. For usual metals, temperature dependence of transport and thermodynamic quantities, such as resistivity and specific heat, obey Fermi liquid theory which predicts specific heat to have linear Temperature dependence and resistivity to T-square. But those quantities of NFL materials have strange T-dependences. This strange state happens when one suppresses transition temperature of antiferromagnetic order (T_N) to zero by applying pressure or magnetic field or doping impurities. Now many condensed matter scientists are working on how to understand this state and its mechanism. One more thing which is making this very interesting is that unconventional superconductivity (SC) happens often when a material has NFL state at temperatures above SC transition. Many scientists believe that NFL state is a prerequisite for unconventional SC.

Answer 2

Non-Fermi liquid is a term used in condensed matter physics to describe materials or systems that do not behave according to the standard Fermi liquid theory. In a non-Fermi liquid, the quasiparticles, which are responsible for the behavior of particles in a Fermi liquid, do not obey the usual rules of quantum mechanics or exhibit the expected properties. This unconventional behavior typically arises in systems that are near a quantum critical point or have strong interactions between their constituent particles.